Methane is an abundant hydrocarbon fuel and chemical feed stock, and is expected to remain so for quite some time. It is desirable to upgrade available methane to methyl or higher oxygen atom containing hydrocarbons, such as alcohols, ethers, aldehydes, etc. Existing technologies for converting methane to methanol include destruction of methane to form a synthesis gas (H.sub.2 and CO), followed by indirect liquefaction steps.
However, conventional catalytic approaches to produce methanol from methane typically have poor conversion efficiencies 18 (25% max.), slow reaction rates, and are not economically competitive because they are typical so energy intensive. One such process, the oxidative coupling process, involves the use of an oxidant to abstract hydrogen from methane and coupling two or more hydrocarbon radicals to form light olefin, oxygenates, and other hydrocarbons. The oxidants are oxygen, halogens and reducible metal oxides as oxygen carriers and catalysts. In the oxidative coupling processes, hydrogen abstraction at the oxygen centers of the catalyst is typically the rate determining step, and catalyst properties are important for end product selectivity. Therefore, the maximum rate of product conversion strongly depends on the rate of radical formation on the active oxygen centers. In order to increase the rates, chemists have used high temperatures, even in excess of 900.degree. C. However, this undesirably promotes deep oxidation of methane to fully oxidized species, such as CO.sub.2.
In another strategy, a high temperature dehydrogenation coupling process has a very high radical generation rate, and correspondingly a high rate of light olefin formation. However, the process is plagued by solid carbon formation which lowers the efficiency of the olefin production, and excess hydrogen is necessary to suppress the solid carbon formation.
It would be desirable to enhance the rate of methane activation for conversion to liquid oxygenated hydrocarbons.